Devices for electrostatically charging coating material that is atomized by a rotary atomizer or spray gun and sprayed towards a workpiece are generally known. Such coating devices typically include a conduit for bringing pressurized coating material within the device to a spray head or rotating cup to atomize the coating material. In the case of rotary atomizers, in the past the entire atomizer including the rotating cup have been constructed from metal and charged to a high voltage to charge the coating material as it is being atomized and sprayed from the edge of the spinning cup. The charged, atomized coating material particulate is dispensed forwardly towards a workpiece that is typically hung from a conveyor by a suspending member such as a hook or the like. The workpiece is typically connected through the hook and a conductive member associated with the conveyor to an electrical ground. The charged atomized coating is attracted to the electrically grounded workpiece to completely coat it due to electrostatic effect.
The spray heads or rotary cups which atomize the coating material, spray or throw the atomized coating in a tangential direction relative to the particulate flow path towards the workpiece producing a spray pattern that is larger than the workpiece to ensure that the surface of the workpiece is completely coated. Atomized particles which are not deposited onto the workpiece are called overspray. The greater the amount of overspray from the dispensing device the less the transfer efficiency of the coating material (i.e., the proportion of the paint sprayed which is actually applied to the workpiece).
Moreover, overspray will either fall by gravity to the floor, be carried by air currents to the overspray control system, or be attracted to other grounded objects in the vicinity of the overspray such as the booth ceiling, and conveyor. Where overspray is allowed to accumulate on conveyor hooks, the electrical grounding connection between the hooks and the workpieces can be reduced or lost in which case even more overspray is produced because the charged particles are no longer attracted to the workpieces.
This problem has been solved with the metal rotary atomizers of the prior art described above by including a metal rod, charged to the same potential as the atomizing cup, located above the rotary atomizer and below the ceiling to repel the charged particles away from the ceiling and conveyor and towards the workpiece. Since the entire rotary atomizer has in the past been a highly charged, sizeable piece of metal equipment, it has been necessary to enclose it in a protective fence with interlocks which cut power to the atomizer when any access doors in the fencing are opened to protect operators. The metal repulsion rods described above, normally equipped with a row of sharp pins projecting from them, have also been highly charged and sizeable pieces of metal equipment and so they also have been located within the protective fencing.
Recently, a low capacitance electrostatic rotary atomizer, constructed substantially entirely from non-metallic components, has been made commercially available which does not present shock hazards to operators, and consequently, has not required protective fencing or electrical interlocks. With this type of rotary atomizer, the placement of a metal repulsion rod above the atomizer to control overspray by repelling the paint particles towards the workpiece and away from the ceiling and conveyor, would create a safety hazard requiring protective fencing and interlocks which deprives the user of the advantage of having a low capacitance, safe rotary atomizer.